Amplifiers of electric signals frequently use an amplifying element such as a transistor or silicon controlled rectifier which is operated alternately in a state of nonconduction, and in a state of full conduction in which a saturation current or near saturation current is flowing in the amplifying element. Such operation of the amplifying element minimizes the product of voltage times current and, hence, minimizes the dissipation of power in the amplifying element itself while permitting a maximum amount of power to be coupled to a load. Assuming, by way of example, that the amplifying element is a transistor, it is well known that the idealized condition of no power dissipation within the transistor itself is not obtained but, rather, power is dissipated in the transistor during the rise and fall times of a signal waveform as well as by the introduction of and removal of electric charges in the base-emitter region of the transistor.
A problem arises in that ever increasing power capability is required of amplifiers used in communication systems such as in underwater sonic signaling systems wherein higher powers of radiated sonic energy are desired for longer range communication. A single transistor may be unable to provide the desired power and a plurality of transistors need be coupled to the load with the resulting danger, particularly in a bridge type circuit, that an imbalance in the signals instantaneously present in each of the transistors may cause the destruction of one of the transistors.
A further problem results from the fact that a transistor amplifier wherein the transistors are alternately driven in states of conduction and nonconduction, while being capable of retaining phase data of the signal being amplified, removes all variations in the amplitude of the signal and thereby destroys amplitude data. This is disadvantageous in an application wherein it is desired to apply a signal of varying amplitude to the load.